The present invention relates to conveyor rollers rotating on fixed shafts in a frame and having internally mounted bearings at each end, and specifically relates to conveyor rollers used where dust and moisture create a corrosive environment, yet where conveyor cleanliness is of prime concern. An example of such an application is a soft-drink beverage bottling and packaging facility. Under normal operating conditions, each roller is subjected to periodically loading and resulting shaft deflection as a package travels across a conveyor. However, during periods of increased production, each roller may be subjected to almost continual load and shaft deflection.
Conventional rollers utilize journal bearings or antifriction bearings such as ball bearings which are subject to misalignment or a loss of bearing surface contact when the roller shaft deflects under load. When bearing surface contact is decreased, more load is distributed over less bearing area, increasing friction and operating temperature. In the case of ball bearings, a deflection of the roller shaft of only 11/2.degree. causes the individual balls to become pinched between the inner and outer races. This additional load on the bearing causes a significant increase in friction as well as a corresponding increase in roller temperature. Conventional conveyor roller bearings deteriorate much faster during extended periods of this type of shaft deflection.
An additional drawback of conventional conveyor rollers is their tendency to build up a charge of static electricity which attracts a layer of process residue on the surface of the roller. This accumulated layer has a tendency to abrade the surface of cartons passing over the rollers, thus significantly decreasing package quality. This problem is more pronounced with steel rollers whose surface accumulates the residue and consequently often cuts the package material. Attempts to coat steel rollers with rubber or plastic have normally proved too costly. It is also fairly common for plant maintenance personnel to encounter debilitating shocks from contacting rollers which have built up a residual electric charge. Conventional rollers are also less desirable because of the potential for spontaneous explosions caused by the ignition of ambient dust by static sparks.
An additional drawback of conventional conveyor rollers is the quite objectionable excessive noise they produce during periods of peak production. Also, recently introduced legislation regulating conditions affecting worker health and safety has given the goal of eliminating both excessive noise and static electricity increased importance.
In an attempt to address some of the above-identified problems, rollers have been constructed from polymeric material. However, the mere substitution of polymers for conventional steel rollers and bearings has generated new difficulties, such as the inability of polymeric bearings to withstand heat, and a persistence of the static electricity problem in the roller area.
Thus, there is a definite need for a conveyor roller and bearing capable of quiet, static-free operation as well as being capable of withstanding shaft deflection on the order of 5.degree. without generating excessive heat and friction. There is also a need for a conveyor roller which is easily installed into a conveyor frame.
It is therefore a major objective of the present invention to provide a conveyor roller designed to rotate on a fixed shaft and having internally mounted bearings capable of accepting the maximum of normally encountered shaft deflection without suffering a loss in bearing surface contact (i.e., load bearing capacity) and a concomitant increase in friction.
Another objective of the present invention is to provide a conveyor roller bearing designed to generate a minimum amount of excess heat and to more readily dissipate whatever amount of heat is generated.
A further objective of the present invention is to provide a conveyor roller which does not generate static electricity.
A still further objective of the present invention is to provide a conveyor roller which generates a minimum of operational noise.
Another objective of the present invention is to provide a conveyor roller which is easily installed in a conveyor frame.